1. Field of the Invention
The present invention relates generally to high activity catalysts based upon gamma alumina containing substrates impregnated with one or more catalytically active metals, processes for preparing the same and uses thereof. More specifically, the present invention relates to process for improving the activity of such catalysts, the improved activity catalysts produced thereby, and various specific catalysts and uses thereof.
2. Description of Related Art
The art relating to particulate porous gamma alumina containing supports, impregnating such supports with various catalytically active metals, metal compounds and/or promoters, and various uses of such impregnated supports as catalysts, is extensive and relatively well developed. As a few of the many exemplary disclosures relating to these fields may be mentioned the following United States patents, all of which are incorporated herein by reference for all purposes as if fully set forth--U.S. Pat. Nos. 2,935,463, 3,032,514, 3,124,418, 3,152,865, 3,232,887, 3,287,280, 3,297,588, 3,493,493, 3,749,664, 3,778,365, 3,897,365, 3,909,453, 3,983,197, 4,090,874, 4,090,982, 4,154,812, 4,179,408, 4,255,282, 4,328,130, 4,357,263, 4,402,865, 4,444,905, 4,447,556, 4,460,707, 4,530,911, 4,588,706, 4,591,429, 4,595,672, 4,652,545, 4,673,664, 4,677,085, 4,732,886, 4,797,196, 4,861,746, 5,002,919, 5,186,818, 5,232,888, 5,246,569 and 5,248,412.
While the prior art shows a continuous modification and refinement of such catalysts to improve their catalytic activity, and while in some cases highly desirable activities have actually been achieved, there is a continuing need in the industry for even higher activity catalysts, which are provided by the present invention.
As an example of this need may be mentioned the need for a higher activity first stage hydrocracking catalyst. In a typical hydrocracking process, higher molecular weight hydrocarbons are converted to lower molecular weight fractions in the presence of a hydrocracking catalyst which is normally a noble metal impregnated silica-alumina/zeolite. State-of-the-art hydrocracking catalysts possess a very high activity and are capable of cracking high volume throughputs. Such catalysts, however, are highly sensitive to contaminants such as sulfur, metals and nitrogen compounds, which consequently must be removed from the hydrocarbon stream prior to the cracking. This is accomplished in first stage hydrocracking processes such as hydrodenitrogenation, hydrodesulfurization and hydrodemetallation. Hydrotreating catalysts utilized in these processes are typically a combination Group VIB and Group VIII metal impregnated alumina substrate. State-of-the-art hydrotreating catalysts, however, are not sufficiently active to allow processing of the same high volume throughputs as can be processed by the hydrocracking catalysts. As such, the first stage hydrocracking processes form a bottleneck in the overall hydrocracking process, which must be compensated, for example, in the size of the hydrotreating unit relative to the hydrocracking unit.